One of the reasons that we love the Porsche 997 Turbo/GT2 so much is their Variable Turbine Geometry's reduced lag. This, coupled with Variable Valve Lift and Timing(on the intake cam, at least) help this engine deliver smooth and powerful performance throughout it's range of RPM. Let's take a closer look at why this is so badass.
Porsche's VarioCam Plus
VarioCam Plus is Porsche's unique way of utilizing your engine's oil pressure to activate an adjustment inside an variable camshaft sprocket to actively(while the engine is running) adjust camshaft timing(see the change in red below). Changes in valve lift occur when oil pressure is directed to affect the two-stage lifters. These lifters will lock and open the valves further with the help of special camshafts thus increasing output.
These adjustments to cam timing and valve lift are activated by the DME(engine control unit) by way of solenoids that open, allowing pressurized oil flow into their given chambers. When this activation is interrupted for any reason, the DME registers a fault.
Fault Code P0021
This fault occurs when camshaft timing activation is inhibited. There are several reasons that this fault could occur but the most common reason is blocked oil flow into the variable cam sprocket. When this happens, the camshafts must be removed and repaired/replaced in order for the fault code to clear.